1. Field of the Invention
The invention relates to manufacturing in-situ coated thermoplastic lens, by applying a coating solution to the surface of ophthalmic lens while it is still in the mold.
2. The Prior Art
In-situ coating via a direct injection process, so called in-mold coating was originally developed to improve the surface appearance of fiber reinforced thermosetting composites such as SMC and BMC parts. In relatively more recent years it's been applied to injection molded thermoplastic parts.
For the regular injection molding process, the thermoplastic piece is ejected out of the mold once it is rigid enough to resist the deformation caused by ejection. In-situ coating injection integrates with injection molding by injecting thermoset coating liquid on the exterior surface of the thermoplastic piece when the thermoplastic piece is solidified to the degree that it won't be damaged by the coating injection. More coating is injected after the desired surface coverage is obtained to achieve certain coating thickness.
This method of in-mold coating has an advantage, in that the coating is able to cure at the same time as the part is cooling. Since access to the part is limited, most of these systems introduce the coating at the top of the mold cavity with the coating injector being located near the parting line. Generally, the molding machine configurations having a vertical parting line, with the movable mold half being reciprocated in a horizontal direction. An example of such machine configuration can be readily seen in U.S. Pat. No. 6,180,043. This patent is concerned with high gloss, opaque coatings, containing as much as 30% and up to 45% titanium dioxide and other pigments. Clearly, for such coatings in which one sees only a highly reflective outer surface, there is no requirement for uniformity or transparency, as with an optical coating.
In patents and publications such as: U.S. Pat. No. 6,676,877, WO 2004/048068, US 2003/0077425, 2003/0082344 (corresponding to International Publication WO 03/035354) and US 2003/0099809, a method of in-mold coating without opening the mold is disclosed. Several specially designed features of the mold such as coating containment shroud were described. These features can prevent coating solution from contaminating the molten resin in the barrel of the injection molding machine or leaking from the parting line. However, since coating is injected into a no-gap cavity filled with thermoplastic, a high coating injection pressure is required. In addition, there is no requirement for coating thickness uniformity or transparency, as with an optical coating.
U.S. Pat. No. 5,943,957 discloses a method for pad printing inked images onto injection-molded pieces while they are still in the mold. The patented method relates to conventional ink that air dries, and does not involve an optical grade coating that will be spread over the lens by re-clamping the mold inserts and allowing the coating to cure via the retained heat in the mold block. Published U.S. Patent Application 2003/0152693 discloses pad printing of lenses, but applies a UV or microwave curable coating on cast lenses which are totally divorced from any contact with an injection molding machine.
The present invention provides a method to apply coating on the surface of ophthalmic lens while it is still in the mold. Coating is thermally cured by the heat from the mold and the residual heat from the thermoplastic lens.